This invention relates to a coil spring supporting grid structure and to a spring unit assembly of the type used in mattresses, foundation units or other items of upholstered furniture.
The present invention will be described in connection with a box spring or foundation unit, but it will be appreciated that the invention has application to other spring unit assemblies where a snap-in connection is desired between the springs and the surface reinforcement structure.
In the assembly of a box spring foundation unit, the coil springs are mounted on a wooden frame and then a top reinforcing and spring supporting structure, consisting of an outer border wire and a multiplicity of intermediate wires or bands, is laid on the top of the coil springs and attached by means of clips, pigtail wires or the like. Various alternative means for attaching the top surface supporting assembly to the springs have been proposed, such as, for example, bending portions of the top convolutes of the coil springs around the traversing wires, or, conversely, bending portions of the traversing wires around the top convolute of the coil springs. The foundation unit thus assembled is usually then shipped to the mattress factory where the upholstery is put on the unit.
The assembling of the box spring by applying hog rings, pigtail wires, clips, or by deforming portions of either the coil spring or the traversing wires of the surface support is an expensive and tedius operation involving considerable cost either in material, or in the amount of labor involved in the assembly operation, or both. In addition, since the assembly operation requires some skill and expertise, it can usually be done only by the spring manufacturer, which means that the unit must be shipped to the mattress company only after it has been fully assembled by the spring company. Such shipment of box springs in the assembled condition is very expensive. In an effort to reduce the expense of shipping the assembled product, companies have resorted to shipping the assembled units under compression in order to save space. This increases the cost of packaging and is somewhat dangerous, because care must be taken in removing the compressive force when uncrating the box springs. However, even when compressive force is used, there is a considerable amount of wasted space in the box spring package.
It is, of course, recognized that if the springs and the surface reinforcing structures could be packaged separately, there would be a substantial saving in the space required to ship the box spring and the shipping costs could be reduced. However, the box springs would then have to be assembled at the mattress factory. As a result, there have been various suggestions in the past with respect to facilitating the interconnection between the coil springs and the surface reinforcing structure or structures. However, these suggestions have involved either a forming operation or an assembly operation which requires additional wires, clamps or the like for attaching the coils to the top supporting assembly.
It is an object of this invention to provide a coil spring supporting grid structure which is adapted for snap-in interconnection with the coil springs, thereby avoiding the expense of additional materials for clamping or tying the coil springs to the supporting structure and minimizing the time and skill necessary in the assembly operation. Because the structure provides a firm, reliable and fast interconnection without requiring additional material, there is a saving in the cost of material, in the cost of assembly, and in the cost of shipping. The components of the structure may be shipped separately, with the coils nested, there can be approximately a 50% saving in space, and it is not necessary that the coils be placed under compression.